What does “40 percent lower” mean in people?

Absolute difference = comparison-group risk × relative change. Number needed to treat (or harm) = 1 ÷ the absolute difference, rounded up to a whole person. Both hold for the length of the study the figures came from.

An odds ratio is converted exactly: with the comparison-group risk p, the treated-group risk is OR × p ÷ (1 − p + OR × p), and the result shows the risk ratio that gives. A hazard ratio How often an event happened in the treated group compared with the control group over the same period. A ratio of 0.80 means 20 percent fewer events. is treated as a risk ratio, which is close when the event is uncommon over the study period and drifts when it is common; the result says so.

This is arithmetic on the two numbers entered. It does not check them against any study, and a converter cannot tell whether the study behind them was a good one. Each EBL record shows its own absolute effects where the trial papers give them.